var goto_top_html="";
goto_top_html+="<div id='goto_top'>";
goto_top_html+="	<div class='btn'>";
goto_top_html+="    	<div class='tip'>";
goto_top_html+="    		<img alt='返回顶部' src='images/back-tip.png'>";
goto_top_html+="    	</div>";
goto_top_html+="    	<img alt='返回顶部' src='images/goto_top.png'>";
goto_top_html+="    </div>";
goto_top_html+="</div> ";

document.writeln(goto_top_html);

var gotoTopDiv = document.getElementById("goto_top");
if(gotoTopDiv!="undefined"){
	gotoTopDiv.onclick=function(){
		goTop(0.5,1);
		return false;
	}
}

/**
 * 回到页面顶部
 * @param acceleration 加速度
 * @param time 时间间隔 (毫秒)
 **/
function goTop(acceleration, time) {
	acceleration = acceleration || 0.1;
	time = time || 16;
 
	var x1 = 0;
	var y1 = 0;
	var x2 = 0;
	var y2 = 0;
	var x3 = 0;
	var y3 = 0;
 
	if (document.documentElement) {
		x1 = document.documentElement.scrollLeft || 0;
		y1 = document.documentElement.scrollTop || 0;
	}
	if (document.body) {
		x2 = document.body.scrollLeft || 0;
		y2 = document.body.scrollTop || 0;
	}
	var x3 = window.scrollX || 0;
	var y3 = window.scrollY || 0;
 
	// 滚动条到页面顶部的水平距离
	var x = Math.max(x1, Math.max(x2, x3));
	// 滚动条到页面顶部的垂直距离
	var y = Math.max(y1, Math.max(y2, y3));
 
	// 滚动距离 = 目前距离 / 速度, 因为距离原来越小, 速度是大于 1 的数, 所以滚动距离会越来越小
	var speed = 1 + acceleration;
	window.scrollTo(Math.floor(x / speed), Math.floor(y / speed));
 
	// 如果距离不为零, 继续调用迭代本函数
	if(x > 0 || y > 0) {
		var invokeFunction = "goTop(" + acceleration + ", " + time + ")";
		window.setTimeout(invokeFunction, time);
	}
}